Dredges are often used when removing solids or semi-solids such as sludge, slurries and sediment from the bottom of a body of water. Such dredges mechanically agitate and pump material settled on the bottom of such a body of water. In order to be effective, dredges must move across the surface of the area to be dredged. This area may have varying depths, with varying bottom firmness, complicating the use of typical propeller or track propulsion methods.
Traditional dredging apparatus traverse an area to be dredged by a series of parallel, linear sweeps of the dredging area. Each traversal entails movement of the dredge in a forward direction while actively dredging material from the bottom, then reversing the dredge by passively drawing it backwards over the path just dredged. Material is not dredged during the passive return trip as dredging only occurs in the forward direction of travel. Each parallel traversal of the area occurs laterally displaced from the previous traversal by a distance approximately the same as the width of the dredging head. In this manner, a dredge makes a series of passes back and forth across the area to be dredged while slightly displacing each pass from the previous one to effect full coverage of the area to be dredged.
Further, even when depth conditions permit underwater coverage of the area to be dredged.
Further, even when depth conditions permit underwater propulsion, continuous forward movement is constrained by the turning radius afforded by the propeller or drive mechanism. Accordingly, it may be difficult to effect a series of parallel, linear dredging passes to ensure complete and non-redundant coverage of the bottom area.
An overhead propulsion mechanism attached to a cable or other suspension above the water surface and anchored to mounting points on the perimeter of the dredging area can provide a propulsion mechanism. This arrangement powers the dredge without requiring propulsion apparatus to accommodate variations in depth and solidity beneath the surface.
A typical overhead propulsion system for such dredges comprises a winch attached to an overhead cable. The winch draws the dredge across the dredging area, then reverses and draws the dredge back. However, as the dredging operation only occurs in one direction, the return pass does not effect any removal of material. After an active dredging pass, the dredge passively returns to the starting side. As the return pass of the dredge does not effect further removal of material to be dredged, the number of passes which need be made is increased approximately twofold. It would be beneficial to provide a dredging machine capable of active dredging in both directions across an area to be dredged.